bio_electric potential waveforms

8/10/2019 Bio_Electric Potential Waveforms

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B IO E LECTRIC P OTENTIAL

W AVEFORMS BY: Asst.Prof.Harshul Thakur

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INTRODUCTION

The instruments measuring physiologicalvariables has name end with suffix gram .

Like ECG( Electro cardiogram),EEG(Electroencephalogram) andEMG(Electromyogram ) etc

The suffix gram is connected to that instrumentname, which is used to measure potentials andgraphically reproduce the waveforms.

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ECG (E LECTROCARDIOGRAM )

It is the name of the waveform resulting from theheart electrical activity.

To understand the origin of ECG, it is necessaryto have some familiarity with the anatomy aswell as physiology of the heart.

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Sinoatrial (SA) nodePacemaker cells

Internodal tractsTransport to AVnode

Bachmans Bundle Right atrium to leftatrium

Atrioventricular (AV)nodeTime delay

Bundle of HisTransport fromatria to ventricles

Bundle branches

Distribution withinventriclesPurkinje network

End fibers tomuscle units

C ARDIAC C ONDUCTION S YSTEM

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E LECTROCARDIOGRAM (ECG)

Figure Representative electricactivity from various regions of theheart. The bottom trace is a scalarECG, which has a typical QRSamplitude of 1-3 mV. (by Frank H.Netter, M. D.)

ECG waveformP wave:atrialdepolarization

QRS complex:ventriculardepolarizationT wave:ventricularrepolarization

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The wave shows the heart's upper chambers (atria) contracting (depolarization)The QRS is combination of re-porization of atria and depolarization of ventricles ,both act almost simultaneouslyThe T wave shows the heart's lower chambers (ventricles) relaxing (repolarization)The U wave believed to be due repolarization of ventricular papillary muscles.

Q interval represents the time interval during which excitation wave is delayed inthe fibers near the AV node.

SA node activates first the rightand then the left atrium.

AV node delays a signal comingfrom the SA node before itdistribute it to the Bundle ofHis.

Bundle of His distribute signalto left bundle branch and rightbundle branch

then Purkinje fibers activatethe right and left ventricles

A typical QRS amplitude is 1-3mV

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EMG(E LECTROMYOGRAM )

The bioelectric potentials associated with muscleactivity constitute the electromyogram.These are measured at the surface of the body.

EMG measurements are done to obtain amountof activity of a given muscle or a group ofmuscles.

Some times the larger muscles may interfere thesmaller muscles, where this is the problem ,needle electrodes inserted directly into themuscle for EMG.

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CONT

The amplitude of the measured EMG waveformsis the instantaneous sum of all action potentialsgenerated at a given point.

The action potential occurs in both +ve and vepolarities at a given pair of electrodes, theysometimes add or sometimes cancel.

Thus EMG waveform appears very much like arandom-noise waveform, with energy of thesignal a function of the amount of muscleactivity.

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Typical EMG waveforms are shown in figure:

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THE E LECTROENCEPHALOGRAM (EEG)

The recorded representation of bioelectricpotentials generated by the neuronal activity ofthe brain is called electroencephalogram.

The EEG has a very complex pattern , which ismuch more difficult to recognize than the ECG.

A typical sample of EEG is shown in next slide..

The waveforms varies greatly with location of themeasuring electrodes on the surface of the scalp.

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CONT ..The experiment has shown that the frequency ofthe EEG seems to be affected by the normalactivity of the person.

A drowsy person, particularly whose eyes areclosed often produces a large amount rhythmicactivity in the range of 8 to 13 Hz.

As a person begin to fall asleep the amplitude

and frequency variation occurs.In light sleep: Large amplitude and low frequencywaveform occurs.Deeper sleep: Even slower frequency but higheramplitude wave occurs.

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CONT ..

The period of high frequency EEG that occursduring sleep is called paradoxical sleep .

Another is Rapid eye movement sleep , associatedwith the high frequency EEG is a large amount ofrapid eye moment beneath the closed eyelids.

The various frequency ranges of the EEG havearbitrarily been given Greek letter designations,because seems to the most prominent feature of

an EEG pattern as shown in next slide.

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E LECTROENCEPHALOGRAM

Figure 4.27

Normal Rhythms ,Alpha: 8 - 13 Hz;quiet, resting

,Beta: 14 - 30 Hz;Thinking, activestates

,Theta: 3.5 - 8 Hz:children, frustrated

states ,Delta: below 3.5Hz; deep sleep

Alpha Wave Example

Opening and closingeyes changes level ofactivity; replacementof alpha rhythm byan asynchronousdischarge

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A BNORMAL EEG

Abnormal firing ofcortical neurons

Largeuncoordinatedrepetitivewave fronts

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CLINICAL EEGStandard placementby anatomicallandmarks

System reference: allelectrodes tied by ahigh resistance to acommon point

Differential amplifierconnections:

A separate groundelectrode in one of thefollowingconfigurations:Between two scalpelectrodesBetween one or bothear lobes

Between a singlescalp electrode andthe system reference

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bio_electric potential waveforms

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